Multi-planar (MPR) and three-dimensional (3D) reconstructions of two-dimensional (2D) image slice data can be very helpful to clinicians, particularly in connection with surgical planning. However, current MR imaging techniques for acquiring medical image slices of a patient's region of interest (ROI) are of limited value when high quality MPR and 3D reconstructions are desired. In MR, the slice thickness for a given acquisition is constrained by multiple factors such as sequence, specific absorption rate (SAR) and field of view (FOV). In addition, in MR there is only one “detector,” the coil unit (e.g., the head coil). Since there is only one detector with MR imaging (unlike CT imaging, wherein multi-detector CT scanners can use several detectors to simultaneously acquire image data), acquisition parameters such as base resolution and slice thickness have much more of a direct impact on acquired images. This limits the ability to change parameters readily before and after image acquisition. In MR there is always a trade-off. For example, although a smaller slice thickness will yield better resolution, smaller slice thickness will also result in decreased signal to noise (SNR), thereby leading to increased scan time and SAR. Each sequence therefore has an allowable slice thickness range. In addition, as the slice thickness decreases, other factors such as “cross-talk”may increase, thereby further reducing image quality. This in turn limits the ability to overlap slice information, a problem that has plagued conventional high resolution MR MPR and 3D reconstruction techniques.
In order to produce high quality MPR and 3D images, an overlap of 50% is desirable. For the reasons stated above, traditional MR techniques do not allow for this degree of overlap of 2D images. Currently, the best MR techniques available for generating 3D images are believed to be volumetric acquisitions, where the base image resolution can be quite good. However, as stated above, with the increase in resolution for such techniques, the SNR is decreased, with the end result being that even the most optimal 3D MR sequence cannot compare to the 3D images derived by current multi-detector CT technology. 3D reconstructions derived from 2D MR acquisitions are even more limited. These images, which have limited resolution and poor SNR, do not produce 3D volumetric images with the quality required for many diagnostic assessments.
Additional background information pertaining to MR imaging issues can be found in the following publications, the entire disclosures of each of which are incorporated herein by reference: Sailhan F, Chotel F, Guibal A L, Gollogly S, Adam P, Berard J, Guibaud L: Three-dimensional MR imaging in the assessment of physeal growth arrest, European Radiology, 2004; April 3 [Epub ahead of print]; Klingebiel R, Thieme N, Kivelitz D, Enzweiler C, Werbs M, Lehmann R: Three-dimensional imaging of the inner ear by volume-rendered reconstructions of magnetic resonance data, Archives of Otolaryngology Head and Neck Surgery, 2002; 128:549-53; Lee V S, Lavelle M T, Krinsky G A, Rofsky N M: Volumetric MR imaging of the liver and applications, Magnetic Resonance Imaging Clinics of North America, 2001; 9:697-716; Kleinheinz J, Stamm T, Meier N, Wiesmann H P, Ehmer U, Joos U: Three-dimensional magnetic resonance imaging of the orbit in craniofacial malformations and trauma, International Journal of Orthodontic Orthognath Surgery 2000; 15:64-8; Krombach G A, Schmitz-Rode T, Tacke J, Glowinski A, Nolte-Ernsting C C, Gunther R W: MRI of the inner ear: comparison of axial T2-weighted, three-dimensional turbo spin-echo images, maximum-intensity projections, and volume rendering, Investigational Radiology, 2000; 35:337-42; McKinnon G C, Eichenberger A C, von Weymarn C A, von Schulthess G K; Ultrafast imaging using an interleaved gradient echo planar sequence in Books of Abstracts, 11th Annual Meeting, Society of Magnetic Resonance in Medicine, 1992; 106; Phillips M D, Lowe M J, Lurito J T, Dzemidzic M, Mathews V P: Temporal lobe activation demonstrates sex-based differences during passive listening; Radiology, 2001; 220:202-07; and Haacke E. M., Brown R. W., Thompson M. R. and Venkatesan R.: Magnetic Resonance Imaging Physical Principles and Sequence Design, John Wiley & Sons, 1999.